In a big number of countries, the main supply tanks are external, usually located on building/house roofs. These external tanks are generally connected to a cold water distribution line going directly to the user and to a hot water distribution line connected to internal hot water tanks which are heated by means of a non-renewable source of energy such as electricity or gas. Water inside the internal tanks originates from the external tanks. Internal tanks are generally connected to a thermostat and a heating activator controllable by the user for heating the water to a selected temperature according to the user requirements. When the user selects a given heating temperature, the activator activates the heater connected to the internal tanks every time the temperature inside the internal tanks fall below the selected temperature. Since the internal tanks are generally located in an environment with ambient temperature (around 20 degrees Celsius), the temperature inside the internal tanks will get effected by the ambient temperature and will fall under the user pre-selected temperature resulting in an iterative process of activation/deactivation of the heater. This results in huge consumption of energy (electricity/gas).
Besides, in hot countries such as the Gulf countries, the external temperature can be very hot reaching up to 60 degrees Celsius during the day. External tanks are exposed to the sun during the day, and thus cold water originating from external tanks reach the user very hot if not cooled down by cooling systems before it gets to the end user. When cooling systems are used for cooling water, this would result in enormous energy consumption.
In fact, in such hot countries, water stored inside the internal tanks are generally cooler than the water stored in the external tanks. The traditional process of heating the water stored in the internal tanks before distributing it to the hot water distribution line from one side, and distributing the water originating from the external tanks to the cold water distribution line is inefficient and results in enormous energy consumption.